Guillotine dampers are used wherever provision must be made to block the flow of exhaust gases through such ducts as those of coal fired electric utility power plants. When such ducts are equipped with gas scrubbers, for example, provision must be made for the servicing without shutting down the boilers. To that end, such ducts are provided with parallel sections in each of which a scrubber is located.
As the servicing of equipment in such duct sections requires the entry of personnel therein, it is essential that they be protected from flowing duct contents by isolating the work area both upstream and downstream thereof as by guillotine dampers.
A guillotine damper has a chamber through which upstream and downstream duct sections are connected. A blade is mounted within the chamber for movement between a first position in which flow through a duct section is unobstructed and a second position in which it blocks the flow. Means are provided to seal the path of the blade when the blade is in its first position and to seal the blade against leakage about its margins when the blade is in its second position.
When the sealing means rely on a constant flow of air under pressure or when seals are frictionally receptive or margins of the blade, the sealing means have not proved to be reliable as in the former case large volumes of air are required and any loss of power results in leakage. Seals engaged by a moving blade are easily damaged with leakage resulting or such seals become ineffective if they become encrusted. Guillotine dampers relying on sealing means of the above types are not adapted for use where zero leakage is a requirement.
An effective construction for sealing purposes is to provide a seat on the downstream side of the blade path and a pressure frame on the upstream side thereof that is provided with a seal engageable with the seat of the blade and movable between a position effecting such sealing engagement into a position enabling the blade to be shifted from one position to the other. To effect such movements of the thrust frame, fluid pressure operated means have been employed to move the pressure frame against the resistance of springs by which thrust frame retraction was effected into operative positions in which it is either held sealed against the seat or the blade and the blade is held against the seat.
In order to avoid the use of energy to maintain the pressure frame in its operative positions, guillotine dampers have had movements of their pressure plates into their operative positions effected by resilient means typically spring packs with frame retraction effected by fluid pressure operated devices with a consequential saving in energy since frame retraction is necessary only when the blade is to be moved from one position to the other. One construction utilized a substantial number of spring packs arranged in closely spaced pairs along the sides of the frame with a retraction jack between each two spring packs.